Tennessee Wastewater Operator Practice Exam

What happens if sulfur dioxide is overfed during the dichlorination process?

1. Increase in effluent pH

2. Drop in effluent DO

3. Increase in effluent chlorine residual

4. Decrease in effluent BOD/COD

The correct answer is: Drop in effluent DO

When sulfur dioxide is overfed during the dichlorination process, it can lead to a drop in effluent dissolved oxygen (DO) levels. This occurs because sulfur dioxide is a reducing agent that can consume oxygen as it reacts with chlorine compounds, leading to a decrease in dissolved oxygen available in the water. The reaction can result in the formation of sulfuric acid, which further contributes to decreased DO levels as the chemical reactions involved can deplete the oxygen from the environment. Monitoring dissolved oxygen levels is crucial in wastewater treatment, as low DO can negatively impact aquatic life and the overall health of receiving waters. Ensuring that the dosing of sulfur dioxide is appropriate is vital for maintaining adequate levels of dissolved oxygen in the effluent. This highlights the importance of careful control and monitoring during the dichlorination process to prevent potential ecological impacts.